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Dynamic light-scattering measurements are reported for suspensions at concentrations in the vicinity of the glass transition. In a mixture of identically sized but optically different particles having hard-sphere-like interactions, we project out the incoherent ͑or self-͒ intermediate scattering functions by adjusting the refractive index of the suspending liquid until scattering from the structure is suppressed. Due to polydispersity, crystallization is sufficiently slow so that good estimates of ensemble-averaged quantities can be measured for the metastable fluid states. Crystallization of the suspensions is still exploited, however, to set the volume fraction scale in terms of effective hard spheres and to eliminate ͑coherent͒ scattering from the structure. The glasstransition volume fraction is identified by the value where large-scale particle motion ceases. The nonequilibrium nature of the glass state is evidenced by the dependence on the waiting time of the long time decay of the relaxation functions. The self-intermediate scattering functions show negligible deviation from Gaussian behavior up to the onset of large-scale diffusion in the fluid or the onset of waiting time effects in the glass.

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Concentrated suspensions of submicron colloidal spheres were studied both by dynamic light scattering and by direct observation of their phase behavior. In agreement with recent theory and computer simulation, the measured dynamic structure factor developed an essentially nondecaying component, implying "structural arrest, " at almost the same concentration as that at which a long-lived amorphous or glass phase was first observed. PACS numbers: 64.70.Pf, 78.20.Dj, 82.70.Kj The idea that sufficiently rapid compression should transform a liquid composed of spherical particles into a long-lived metastable amorphous solid or glass dates back at least to the sphere-packing experiments of Bernal' and Scott and to the free-volume model of Cohen and Turnbull.More recently this simple "glass transition" has been studied in a number of computer experiments.Since 1984 the subject has gained impetus with the prediction of such a glass transition by kinetic and hydrodynamic theories of liquids which incorporate a nonlinear feedback mechanism.The transition from the ergodic liquid state to the nonergodic glass is signaled by divergence of the shear viscosity, by vanishing of the self-diffusion coefficient, and by "structural arrest, " the partial freezing-in of density fluctuations.To date these ideas have not been tested on real systems composed of spherical molecules because compression and/or temperature-quench rates high enough to bypass crystallization in a controllable fashion are not attainable. ' In this Letter we report the observation of a glass transition in concentrated suspensions in a liquid of solid submicron colloidal spheres having a narrow distribution of size. The static ' ' and dynamic ' properties of suspensions of identical spheres have many features in common with those of simple liquids. In particular, the full range of phase behavior, fluid crystal glass, is observed. ' However, the relaxation times of the diA'usive motions of particles in suspension are at least 10 times larger than those of atoms in a liquid. Thus the lifetimes of the metastable fluid phases of suspensions, observed before significant crystallization takes place, can be long enough, minutes to hours (see below), to allow detailed study of their properties. Here we compare measurements by dynamic light scattering (DLS) of F(Q, r) [Eq. (3)], the temporal correlation function of particle-density fluctuations, in the metastable fluid and glass phases with both theoretical predictions ' and a recent computer simulation. ' Good qualitative agreement is observed. Our main finding is that F(g, r) develops an essentially nondecaying component, associated with structural arrest, at almost exactly the same suspension concentration as that at which long-lived colloidal glasses are first observed. ' A useful, if oversimplified, picture of this archetypal glass transition can be given in terms of a neighbor cage in which the motion of individual particles is partially or completely constrained.At normal liquid densities, a particle is ab...

Suspensions of identical particles with hard-sphere-like interactions are studied at concentrations for which the equilibrium state is crystalline. Dynamic light scattering measurements on these suspensions, in their metastable amorphous states prior to crystallization, identify the kinetic glass transition (GT) by the arrest of particle concentration fluctuations on the experimental time scale. This kinetic glass transition coincides with a spectacular change in the mechanism of crystallization from the formation of small crystals, which appear homogeneously nucleated throughout the sample at concentrations below the transition, to the growth, above the transition, of larger and highly asymmetric crystals whose shape and orientation depend on the shear history of the suspension. The intermediate scattering functions are measured over a time window spanning up to eight decades and for several wave vectors near the position of the main structure factor peak. From an analysis of the data in terms of the idealized version of mode-coupling theory, we conclude that both a and P processes are necessary to describe the slow structural relaxation in the fluid near the GT. The superposition principle of the a process, for the colloidal fluid, and the factorization property of the P process, for the colloidal fluid and glass, are verified. PACS number(s}: 64.70.Pf, 61.20.Ne, 82.70.Dd The implied change in the underlying mechanism for flow is apparent in computer simulation studies of supercooled atomic fluids. These studies indicate that the nature of the many-particle dynamics changes from that driven by kinetic processes to that dominated by activated trans-